1. Field of Inventions
The present inventions relate generally to the formation of therapeutic lesions in body tissue.
2. Description of the Related Art
There are many instances where therapeutic lesions are formed in body tissue. One conventional method of forming lesions involves the application of electromagnetic radio frequency (“RF”) energy to heat and eventually kill (i.e. “ablate”) tissue. The ablation energy is typically supplied and controlled by an electrosurgical unit (“ESU”) during the therapeutic procedure. More specifically, after an electrophysiology or electrosurgical device has been connected to the ESU, and the electrodes or other energy transmission elements on the device have been positioned adjacent to the target tissue, energy from the ESU is transmitted through the electrodes to the tissue to from a lesion. The amount of power required to coagulate tissue ranges from 5 to 150 W.
With respect to the formation of therapeutic lesions in heart tissue to treat cardiac conditions such as atrial fibrillation, atrial flutter and arrhythmia, some procedures utilize electrode-carrying catheters which form lesions on the endocardium in order to create a maze for electrical conduction similar to that created by surgical maze procedures. The lesions are carefully placed to interrupt the conduction routes of the most common reentry circuits. Exemplary catheters are disclosed in U.S. Pat. Nos. 6,013,052, 6,203,525, 6,214,002 and 6,241,754. Surgical soft tissue coagulation probes that carry one or more electrodes on relatively short, stiff shafts have also been used in endocardial and epicardial procedures where access to the heart is obtained by way of a thoracostomy, thoracotomy or median sternotomy. Exemplary surgical probes are disclosed in U.S. Pat. Nos. 6,142,994, 6,468,272 and 6,645,200. Electrosurgical clamps have also been used to form lesions around, for example, a pairs of pulmonary veins. Exemplary electrosurgical clamps are disclosed in U.S. Pat. No. 6,142,994 and U.S. Pat. App. Pub. No. 2003/0158547.
One of the advantages associated with electrophysiological and electrosurgical procedures is the rapid nature of the lesion formation after the electrodes have been positioned against the target tissue. Typically, an irreversible transmural lesion will be formed in heart tissue within a few seconds after the energy transmission process is initiated. The present inventor has, however, determined that there may be some instances where the rapid formation of irreversible lesions is undesirable.